During refueling of an automobile, liquid fuel entering the fuel tank displaces gases therein, such as air and fuel vapor. A vent pipe carries the gases to the tank exterior, typically venting directly to atmosphere or, alternatively, to a vapor handling device, such as a carbon canister. When the liquid fuel level covers the vent pipe opening, gases can no longer vent, thus causing a pressure increase which shuts off the fuel pump.
In addition to the just described fuel pump shut-off pressure, fuel tank pressure rises during normal engine operation for a variety of reasons. For example, hot fuel returning from the engine, fuel pump operation within the fuel tank, and normal diurnal temperature changes can increase fuel temperature within the fuel tank. Higher fuel temperature causes an increase in fuel evaporation and thus an increase in fuel vapor within the tank. Increased fuel vapor and fuel temperature can result in fuel tank pressure exceeding atmospheric pressure. With such conditions, sudden removal of the fuel filler pipe cap may result in fuel expulsion through the vent pipe, an obviously undesirable consequence.
The present invention provides a vapor venting apparatus which limits the fuel level within the tank while providing means for reducing fuel flow through the apparatus upon removal of the fuel filler pipe cap after fuel tank pressure increases above atmospheric pressure.